The conclusion was contained in the 82-page final report of an international probe into the alleged chemical weapons attacks in Syria, Xinhua reported.
Use of chemical weapons is grave violation of international law: Ban Ki-moon
The report, originally expected in late October, was posted on the website of the UN Office for Disarmament Affairs shortly after it was presented to UN Secretary-General Ban Ki-moon here Thursday by Ake Sellstrom, the head of an international probe into the alleged use of chemical weapons attacks in the Syrian conflict.
Sellstrom, a Swedish scientist and an expert in chemical weapons, was accompanied by his team leaders from the OPCW and the World Health Organization (WHO) in presenting the report in Ban's conference room at the UN headquarters.
His team is separate from the operation of the OPCW mandated by the UN Security Council (UNSC) in Resolution 2118 in September to rid Syria of chemical weapons by the middle of next year.
The Sellstrom team was set up in response to allegations of chemical weapons being used in Syria by both the government and opposition forces.
UN spokesperson Martin Nesirky said earlier it was up to the UNSC to determine what, if any, course of action was necessary.
Ban commended Sellstrom and his team "for their important and courageous work. They have carried out their tasks with the highest degree of professionalism, and did so in the face of many dangers".
"Much has happened since the first allegations of the use of chemical weapons in Syria in March of this year," the secretary- general said.
"The Syrian government acknowledged that it possessed chemical weapons and subsequently joined the Chemical Weapons Convention," he said.
"An OPCW-UN Joint Mission was established and continues to oversee the timely elimination of Syria's chemical weapons program in the safest and most secure manner possible."
"The use of chemical weapons is a grave violation of international law and an affront to our shared humanity," Ban said. "We need to remain vigilant to ensure that these awful weapons are eliminated, not only in Syria, but everywhere."